1. Sexual Reproduction in Animals
Chapter 17
Sexual Reproduction in Animals

2. Objectives Students should be able to:
Identify on diagrams of the male reproductive system and give functions of testes, scrotum, sperm ducts, prostate gland, urethra and penis
Identify on diagrams of the female reproductive system and give functions of ovaries, oviducts, uterus, cervix and vagina

3. Briefly describe the menstrual cycle with reference to the alternation of menstruation and ovulation, the natural variation in length, and the fertile and infertile phases of the cycle with reference to the effects of progesterone and estrogen only
Describe fertilisation and early development of the zygote simply in terms of the formation of a ball of cells which becomes implanted in the wall of the uterus

4. State the functions of the amniotic sac and the amniotic fluid
Describe the functions of the placenta and umbilical cord in relation to exchange of dissolved nutrients, gases and excretory products (structure details are NOT required)
Discuss the spread of human immunodeficiency virus (HIV) and methods by which it may be controlled

5. 17.1 Sexual Reproduction in Animals
Involves fusion of gametes
Gametes come from different parents
This method is typical of vertebrates

6. Where are gametes formed?
Gametes are produced by special organs called gonads
Male gametes (sperms)  testes (testis)
Female gametes (eggs/ova)  ovaries (ovary)
Involves mating process for sperms and eggs to meet

7. Gametes & body cell
Normal cells have a diploid number (2n) of chromosomes
Gametes have haploid number (n) of chromosomes
Because normal body cells are produced by mitosis
Gametes are produced by meiosis

8. Why should gametes have a haploid number of chromosomes?
Nucleus of human body cell has 46 chromosomes = 23 pairs
23 chromosomes from father, 23 from mother, that is why gametes have only 23 chromosomes. Add up = 46

10. Reproductive System in Man
Male Reproductive System
Functions of important parts
Testes – produces sperms and male sex hormones
Scrotum – held the testes outside the body as production of sperm requires a lower temperature
Sperm ducts – a muscular tube which force sperms through the urethra during copulation

11. Prostate gland – secretes fluid and enzymes which nourish and activates the sperms so that they can swim actively. Mixture of fluid and sperms is called semen
Urethra – passageway for both urine and semen out of the body. Urine and semen do not pass through the urethra at the same time
Penis – an organ used to transfer sperms to the female reproductive organs

14. Female Reproductive System Functions of important parts
Ovaries – organs where eggs/ova and female sex hormones are produced.
Oviducts – provide a passageway for the eggs to travel to the uterus. The place where fertilisation takes place
Uterus – fetus develops during pregnancy
- protects and nourishes the
developing embryo
- muscles contract to push fetus out during
birth

15. Cervix – a ring of muscles which close the lower end of the uterus
Cervix – a ring of muscles which close the lower end of the uterus. It enlarges to allow passage of the fetus during birth
Vagina – a place for the deposition of sperms by the penis. It also serves as a passageway for the baby during childbirth

18. Comparison btw male and female gamete
Sperm
Egg
Size
Smaller in size
Much bigger in size
Numbers
Produced in large numbers each time and throughout the lifetime of the animal
One egg is produced every month and there is a fixed number of eggs at birth
Mobility
Able to swim
Cannot move by itself

19. Menstrual Cycle
A cycle of events that takes place in the female reproductive organs. The average menstrual cycle is about 28 days.
Menstrual cycle can range from 21 to 33 days. This is the natural variation in the length of the menstrual cycle.
The monthly discharge of blood is called menstruation. This usually lasts for 5 days

20. The cycle
Day 1 – 5
Menstruation occurs (uterine lining breaks down and flows out of the body
Day 6 – 13
Oestrogen is secreted which causes the repair and growth of lining of the uterus
The uterine lining becomes thick and spongy with blood vessels

21. Day 14 (Ovulation) Day 15 – 28 Fertile period
Progesterone is secreted.
Some oestrogen is also secreted
Day 15 – 28
Progesterone maintains the uterine lining by causing it to thicken further and be supplied with more blood vessels, preparing it for the fertilised egg
It inhibits ovulation

22. The Cycle …..
If no fertilization occurs, the egg breaks down. Progesterone is not produced and so the uterine lining breaks down. Hence, menstruation begins after Day 28
If there is fertilization, uterus lining will not shed. Instead, it remains and help to support the developing embryo

24. Fertile and infertile periods of the menstrual cycle
Fertilisation is possible from day 11 to 16. This is the fertile period
The rest of the days make up the infertile period of the menstrual cycle
(above mentioned is just a guideline because mentrual cycle can be affected by factors such as stress and malnutrition)

25. Fertilisation
The egg released form the ovary is usually surrounded by a few layers of follicle cells.
follicle cells
Figure page 325

26. Fertilisation
The egg released form the ovary is usually surrounded by a few layers of follicle cells.
follicle cells
egg nucleus
enzymes released by sperm
sperms
Figure page 325
To penetrate the egg, the acrosome of the sperm releases an enzyme to disperse the follicle cells and break down part of the egg membranes for the sperm to enter. 1

27. Fertilisation
The egg released form the ovary is usually surrounded by a few layers of follicle cells.
follicle cells
egg nucleus
follicle cells dispersed
enzymes released by sperm
only one sperm nucleus enters the egg
sperms
Figure page 325
To penetrate the egg, the acrosome of the sperm releases an enzyme to disperse the follicle cells and break down part of the egg membranes for the sperm to enter. 1

28. Fertilisation
The egg released form the ovary is usually surrounded by a few layers of follicle cells.
follicle cells
egg nucleus
follicle cells dispersed
enzymes released by sperm
only one sperm nucleus enters the egg
sperms
Figure page 325
To penetrate the egg, the acrosome of the sperm releases an enzyme to disperse the follicle cells and break down part of the egg membranes for the sperm to enter.
Only one sperm nucleus enters the egg. The haploid sperm nucleus fuses with the haploid egg nucleus, and a fertilised egg or diploid zygote is formed. 1 2

29. Fertilisation
The egg released form the ovary is usually surrounded by a few layers of follicle cells.
follicle cells
egg nucleus
follicle cells dispersed
diploid nucleus
zygote
enzymes released by sperm
The haploid nucleus of the sperm fuses with the haploid nucleus of the egg to form a diploid zygote.
only one sperm nucleus enters the egg
sperms
Figure page 325
To penetrate the egg, the acrosome of the sperm releases an enzyme to disperse the follicle cells and break down part of the egg membranes for the sperm to enter.
Only one sperm nucleus enters the egg. The haploid sperm nucleus fuses with the haploid egg nucleus, and a fertilised egg or diploid zygote is formed. 1 2

30. Fertilisation
The egg released form the ovary is usually surrounded by a few layers of follicle cells.
follicle cells
egg nucleus
follicle cells dispersed
diploid nucleus
zygote
enzymes released by sperm
The haploid nucleus of the sperm fuses with the haploid nucleus of the egg to form a diploid zygote.
only one sperm nucleus enters the egg
sperms
Figure page 325
To penetrate the egg, the acrosome of the sperm releases an enzyme to disperse the follicle cells and break down part of the egg membranes for the sperm to enter.
Only one sperm nucleus enters the egg. The haploid sperm nucleus fuses with the haploid egg nucleus, and a fertilised egg or diploid zygote is formed.
As soon as the sperm has entered the egg, the membrane of the egg changes so that no other sperms can enter. The remaining sperms, which do not fertilise the egg, eventually die. 1 2 3

31. Development of the embryo
Fertilized egg passes along the oviduct to the uterus
Meanwhile it begins to divide to form a hollow ball of cells called embryo
The embryo reaches the uterus and implants itself to the uterine lining

33. Subsequently, membranes develop to enclose the embryo.
The embryo is enclosed in the amniotic fluid which has the functions:
Supports and cushions the embryo before birth
Shock absorber
Protects embryo against mechanical injury
During birth, it lubricates and reduces friction n the vagina
It buoys up the fetus and allows it to move freely during growth

34. Villi grow from the embryo into the uterine wall
The villi and the uterine wall in which the villi are embedded make up the placenta
Placenta is formed partly from embryonic tissue and partly from the uterine lining
The umbilical cord attaches the embryo to the placenta

36. Functions of Placenta
Allows dissolved food substances and oxygen to diffuse from the mother’s blood into that of the embryo
Allows metabolic waste products to diffuse from the embryonic blood capillaries into the mother’s bloodstream
Allows antibodies to diffuse from the mother’s blood into the embryonic blood capillaries
Produces progesterone which maintains uterine lining in healthy state during pregnancy

37. Functions of umbilical cord
Contains 2 umbilical arteries that transport deoxygenated blood and metabolic waste products such as urea from the fetus to the placenta
Contains 1 umbilical vein that transports oxygenated blood and food substances such as glucose and amino acids from the placenta to the fetus
**Exchange of substances is through diffusion

39. Sexually Transmitted Diseases
May be spread through sexual intercourse
May also be transmitted through direct skin contact or when blood from an infected person gets into the bloodstream of an uninfected person
STDs are caused by bacteria or viruses
Can result in physical damage or even death

40. Acquired Immune Deficiency Syndrome (AIDS)
Caused by Human Immunodeficiency Virus (HIV)
HIV destroy the body’s immune system. Hence, infections which are normally mild may prove to be fatal to a person with AIDS

41. Signs and symptoms Chronic or persistent fever
Severe diarrhoea lasting for months
Pneumonia
Kaposi’s sarcoma (cancer of the blood vessels)
Brain infection
Widespread tuberculosis

42. Mode of transmission Sexual intercourse with an infected person
Sharing needles with an infected person e.g. drug abuse, tattooing, acupuncture, ear-piercing
Blood transfusion from infected person
During pregnancy from infected mother to fetus

43. AIDs
Is not spread through toilet seats, door knobs, coughs, swimming pools or mosquitoes

44. Prevention and control
Keep to one sex partner or do not have sex
Males to wear condom
Avoid drug abuse
Avoid sharing instruments that are likely to break the skin and be contaminated with blood
Go to reliable operators for services such as tattooing, acupuncture

45. 4.1 D
MCQ
1 D
4 C
6 C
7 D
10 A
11 A
12 C
13 C
14 B
17 C

46. Paper 2 2
P: Sperm Organ: Testis
Q: Pollen Organ: Anther

47. 2(b)
R is the tail and it enables the sperm to swim up the female reproductive system to fuse with the egg.
S is the pollen tube. It grows into the style all the way to the ovary. It guides the male gamete to the ovule for fusion to take place.

48. 2(c)
Similarities: T is the nucleus and it contains chromosomes
Differences: T contains only half the number of chromosomes